@ifitaintboeing- Thanks for the link, that makes more sense now.
@Ultranomad- that's a good question... I got my PPL under JAR, and during the training I got signed off VP on a Slingsby; but was told that was a definite 2 year validity.
A couple of years ago I wanted to go to the states for a flying holiday, the group I wanted to go with have FAA licences, and did a deal for multi-aircraft rental from an FBO. The aircraft had EFIS/VP and fixed gear, because my friends had FAA Licences they therefore only required a checkout on the aircraft in order to fly the "complex" aspects. I was trying to find what I would have to do wrt the Differences Requirements and I ended up getting a range of different answers to my questions about my differences validity on a JAR-PPL.
1) Is the VP sign-off still valid? Answers ranged from yes, because it piggy backs an SEP(A) to no that it is only valid for 2 years. (The linked document does seem to advise that the Differences on an SEP(A) do not expire - I read in your case, if you are flying complex regularly, you might just need to do an hour with an instructor as worse case)
2) Can an FAA Instructor sign me off on EFIS/VP as part of the rental check out? Again answers ranged from yes, because they won't let me fly until I am safe; to no-way, the FAA won't cover everything required by JAR Differences training and therefore will require a JAA Instructor to sign it off.
The bottom line was that I got so confused by the whole thing, I pulled out of the trip and did not go... but it did wet the appetite to get the FAA licence, mainly for simplicity... but looks like EASA have scuppered that one!!!